Energy requirements in Alzheimer's disease patients

Weight loss in Alzheimer's patients has been observed by many clinicians and reported in the international geriatric literature. It represents a puzzling challenge for clinicians and researchers, and it is an important issue for caregivers and nursing home staff concerned with state and federal requirements for nutrition and weight monitoring. Using indirect calorimetry, we studied the resting energy expenditure of 21 elderly patients; 12 were residing in a community setting, and 9 were institutionalized. Of the 12 community-living patients studied, 5 had early to moderate Alzheimer's disease, and 7 were nondemented control subjects. Of the 9 institutionalized patients, all were severely demented, bedridden, and fed exclusively by gastric tube in a closely monitored clinical environment with daily bedside weighing. Four had Alzheimer's disease, and 5 had multi-infarct dementia (MID). Among the outpatients, the Alzheimer's group showed increased energy requirements (p = 0.028) and a significantly different pattern of fat-free mass compared with control subjects (p = 0.031). These observations on community-residing elderly were consistent with, and extended by our findings on energy requirements of the demented institutionalized patients. The calorie intake necessary for weight maintenance of the bedridden institutionalized patients was determined during their prolonged institutionalization. The presumed maintenance level of calorie intake was then verified during a 10 wk study. During the 10 wk, we documented no significant change in weight with constant energy intake. Compared with MID patients, Alzheimer's patients tended to weigh less (52.84 vs. 56.4 kg; p = 0.20) but actually required more calories (1626 vs. 1341 kcal, p < 0.011). Calorie intake of the institutionalized Alzheimer's patients was 30.89 kcal/kg compared to 23.18 kcal/kg in the MID control subjects (p < 0.001). These data indicate that energy requirements are greater for Alzheimer's patients than for MID or nondemented control subjects of similar size. The differences appear to be the result of increased lean-body mass in Alzheimer's patients. Further studies are necessary to elucidate the mechanisms leading to their altered body composition.